The present invention relates generally to a method of producing a high critical temperature (T.sub.c) superconducting ceramic material. More particularly, the invention relates to a superconducting ceramic material composed substantially of a single phase prepared by heat treating a starting, glassy ceramic material within a preselected time and temperature transformation region.
High T.sub.c ceramic superconductor materials of the Bi-Sr-Ca-Cu-O system have recently been discovered, and substantial effort has been expended in an attempt to understand the fundamental characteristics of these ceramics. Preparation of the high T.sub.c ceramic materials typically has involved conventional ceramic processing techniques. In particular, work has been directed to the production of the highest T.sub.c phase of Bi-Sr-Ca-Cu-O wherein the T.sub.c is about 110.degree. K., compared to other crystalline phases having T.sub.c values of 20.degree. K. and 85.degree. K. These approaches usually involve heat treatment of sintered polycrystalline materials, but to date there has not been a suitable method devised for reliable Production of significant quantities of the 110.degree. K. phase. Current methods result in sizable quantities (typically more than about 10%) of the lower T.sub.c phases being produced, and these phases cannot be eliminated by conventional heat treatment. Such multi-phase structures have substantial commercial disadvantages compared to a single phase structure having a T.sub.c of 110.degree. K. Such polycrystalline starting materials include various inherent barriers to forming a single phase material, such as grain boundaries and contaminants which are difficult to overcome in order to form the desired single phase structure.